The present invention relates to wireless electronics, and in particular, to wireless communication systems and methods.
Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Communication systems generally contain one or more transmission channels to transmit data from the transmitter to the receiver. The components included in a transmitter and receiver may vary depending on the attributes of the communication channel, the signaling, and the goals of the transmission channel. FIG. 1 illustrates an example of a transmitter 100 used in a wireless communication system. Here, a digital-to-analog converter (“DAC”) 110 receives a digital input signal (“IN”). The DAC converts a digital signal to an analog signal. This may be necessary in communication systems that take advantage of digital signal processing. The DAC is coupled to the input of filter 120. The filter may be used to remove undesirable frequencies and signal images. The filter is then coupled to mixer 130. The mixer may be used to up-convert the frequency of the signal by combining it with a local oscillator signal (“LO”). The output of the mixer is coupled to power amplifier 140 to amplify the signal for transmission before it is sent through antenna 150. The transmitter 100 is limited to up-converting a signal to one center frequency (or modulation frequency), which is the LO frequency. Typically, the amount of information transmitted around the center frequency is limited by the bandwidth of the transmitter around the center frequency. Accordingly, this limits the amount of data that can be transmitted. Typical prior art approaches to improving the information capacity in a wireless communication system involve maximizing the bandwidth around the center frequency to increase the amount of information that may be modulated onto the carrier frequency.
Another limitation to wireless communication involves allowable output power. In many countries, regional authorities will limit the amount of power that may be transmitted at any given frequency or across a range of frequencies. In other words, when a transmitter transmits a signal at a particular center frequency, the transmitter may be required to output less than a specified upper limit of power per Megahertz. This limitation may limit the reliability, the range, and the effective throughput of data transmission. Transmission range, reliability, throughput, complexity, and cost all play a role in enabling new wireless applications. Since there is a continuing need for new wireless devices, these and other issues, concerning the transmission and reception of radio frequency (RF) signals, become important. Thus, there is a need for improvements in wireless communication systems and methods.